We propose a novel method to suppress the emittance variation caused by the opening and closing of the gap of insertion devices (IDs) in extremely low emittance light source storage rings. The core idea is to leak a small amount of dispersion into the straight section where IDs are installed and optimize its value so that the radiation excitation and damping caused by IDs are balanced [1]. A typical value of the leaked dispersion is about 10mm or less, and the storage ring can be considered quasi-achromatic. To carry out the optimization, we introduced a concept of “average ID peak field” over the ring as an indicator of the ID operating condition in user time. This concept allows us to represent a complex ID gap status with a single parameter and is very effective in deriving an equation for determining the optimum value of the leaked dispersion. The proposed method is passive and applicable to any light source storage ring, and the emittance variation is potentially expected to be less than 1% by carefully optimizing dispersion leakage. In this work we show how this scheme works for suppressing the emittance variation using the SPring-8-II storage ring [2] as an example.

We have been developing an in-situ work function (WF) measurement system to investigate an unexpectedly short lifetime problem of a CeB6 thermionic cathode at the SACLA electron injector. Photoelectron yield spectroscopy using a nanosecond tunable pulsed laser in the wavelength range from 410 to 709 nm was adopted because this method provides a high S/N ratio in a hot operational condition of the thermionic cathode and makes it possible to perform the measurement during the XFEL operation. As the first step, demonstrative WF measurements using an offline cathode test system have been conducted and the WF of an unused fresh CeB6 cathode was precisely estimated to be a value of 2.44±0.02 eV at a temperature of 836 °C. In this conference, the details of the test system and the first measurement results will be presented.

In recent years, even accelerators, which are fundamental tools for advanced researches, should be green regarding energy/resource consumption and operation efficiency. How to improve the performance of accelerators in such an environment will be a major challenge for the field of accelerator science and technology. Against this backdrop, we have developed a long-term plan to promote the green-oriented upgrade of accelerator complex at the SPring-8 campus. We have started to integrate and rationalize the two independent accelerator systems, SPring-8 and SACLA, achieving a 20 % energy saving in a synchrotron radiation facility. We will then, as a next step, renovate the current SPring-8 storage ring by incorporating cutting-edge technologies not only to improve its performance but also to significantly reduce energy consumption by half. Upgrade of current SACLA will follow the SPring-8 upgrade. This presentation will describe our strategic accelerator upgrade plan, its progress and achievements, and future developments.

Novel iron lamination with additional interlaminar insulation has been successfully developed for magnet cores of fast kicker magnets in particle accelerators. By minimizing the eddy current induced between core laminas, a pulse profile of the excited magnetic field has been significantly improved up to a few MHz range. The magnet core is formed by alternately stacking thin steel and insulation sheets to avoid electrical contact between the steel sheets on the cutting edge. A pair of test magnets with the new iron lamination was assembled to evaluate magnet performances focusing on applications to matched kickers in the accelerators. The magnetic field pulse profiles of the two magnets have successfully proved to match below 0.1% over the entire pulse duration, which is significantly better than those with conventional iron lamination. The developed fast kicker magnets are promising for the beam injection kickers in the coming next-generation light sources and future colliders, where suppression of the transient stored-beam oscillation during beam injection is crucial.

Coupled-bunch instability arising from impedances of higher-order modes (HOMs) in RF cavities is a problem to be suppressed in high-current, low-emittance electron storage rings. As a countermeasure against the problem, we have developed a compactly HOM-damped cavity resonating in the TM020-mode at a frequency of 509 MHz. The damping structure compromises circumferential and shallow slots in the cavity inner-wall and ferrites inside the slots. Since the slots are along the magnetic nodes of the TM020 mode, the ferrites absorb only RF powers of the HOMs. The cavity has a shunt impedance of 6.8 MΩ and generates an accelerating voltage of 825 kV at a 100 kW input. The cavity has a slot-type input coupler with a variable-length stub to match its coupling degree with change in beam loading during the operation. The prototype cavity demonstrated satisfactory performance in high-power operation up to 120 kW. Therefore, this innovative cavity is about to be utilized for beam acceleration in the new 3 GeV synchrotron radiation facility, NanoTerasu. We report on the performance of four fabricated cavities, problems and countermeasures experienced in their high-power tests.

We developed high-precision digital control magnet power supplies (MPSs) aiming at next-generation light sources such as SPring-8-II. The system consists of a high-precision ADC circuit and an FPGA that processes a proportional-integral control and pulse-width-modulation. Using the system, the current ripple and long-term stability (8 hours) of the MPS are controlled within 20 ppm. The MPS can be made to fit various magnets by readily adjusting feedback parameters. We also developed functions of a pattern mode and a multi-channel synchronization. In the pattern mode, the output current comes in a 0.5 Hz sine-wave that can be applied to a beam-based alignment and other purposes. The multi-channel synchronization can precisely synchronize the timing of three outputs for 6-pole steering magnets etc. The newly develop MPSs have been introduced to the next-generation 3 GeV light source, NanoTerasu, in Japan. There, large current MPSs with 50 - 650 A are used for family magnets, and DC-link type MPSs with +/-5 - 20 A are used for steering magnets in the storage ring, and various magnets in the injector linac. We will report an overview and performances of MPSs.

In everyday the lighting environments is increasingly replacing incandescent and fluorescent bulbs with light-emitting diodes (LEDs), which offer superior electricity-to-light conversion efficiency. In accelerator facilities, too, the time has come to replace conventional lighting with LEDs and other high-efficiency, green lighting. In order to promote the replacement of lighting in an accelerator tunnel, we investigated the process of the radiation damage for commercially available LED lightings in an X-ray radiation environment such as in the electron storage ring SPring-8. It was found that metal-oxide-semiconductor field-effect transistors (MOSFETs) to be supply power for the LED lighting were damaged by X-ray irradiation with the total dose effect greater than several hundred Gy (air kerma). In situ measurements of the MOSFET under an irradiation by an X-ray tube clearly showed a sudden increase of the off-state drain current accompanying with a sharp increase of MOSFET temperature as a function of radiation dose, which eventually caused the device failure. This presentation shows two effective countermeasures for the longer lifetime of LED and application examples.